Locking webpack to a version (#2703)

webapp/package.json

@@ -53,7 +53,7 @@
     "sass-loader": "3.2.0",
     "style-loader": "0.13.0",
     "url-loader": "0.5.7",
-    "webpack": "webpack/webpack#master"
+    "webpack": "2.1.0-beta.5"
   },
   "scripts": {
     "check": "eslint --ext \".jsx\" --ignore-pattern node_modules --quiet .",